1. Field of the Invention
This invention relates to a membrane oxygenator and method of making the same and, more specifically, it relates to a microporous hollow fiber oxygenator and the method of making the same.
2. Description of the Prior Art
In normal healthy human beings and certain animals the lungs function as a means for transfering oxygen to the blood and receiving carbon dioxide from the blood. In many circumstances such as in certain surgical procedures, for example, the individual is unable to function in the desired manner and an oxygenator must be employed to accomplish the necessary transfer of oxygen into the blood and carbon dioxide out of the blood.
One known system of adding oxygen to the blood involves bubbling of the oxygen directly into the blood. The oxygenation process, which occurs through diffusion of oxygen from the bubbles into the bloodstream, is accompanied by diffusion of carbon dioxide from the blood into the bubbles, thus flushing excess carbon dioxide from the blood. One of the difficulties with such a system is that direct contact between the bubbling oxygen and the blood can damage the red blood cells.
It has also been known to provide semi-permeable membranes which permit passage of oxygen and carbon dioxide therethrough, thereby permitting the desired transfer without the objectionable direct contact between the oxygen gas bubbles and the blood. One of the problems which has been experienced with this approach is the fact that the transfer of gases with the blood has been inefficient.
It has also been known to employ rotating disk membrane oxygenator for effecting gas transfer. See U.S. Pat. Nos. 3,413,095 and 3,034,505.
Efforts have also been made to form the membranes into tubular shape and flow the blood through the tubes with the gasous interchange being effected through the tube wall. It has been found, however, that as a result of the rate of flow of blood as related to the permeability rates of the gases the blood flowing toward the center portions of the tube was inadequately oxygenated and inadequately relieved of the carbon dioxide. See generally U.S. Pat. Nos. 3,864,259; 3,893,926 and 3,505,686.
U.S. Pat. No. 4,187,180 discloses a hollow-fiber permeability apparatus which seeks to minimize inefficient interchange between fluid flowing along the exteriors of the hollow fibers and material within the fiber interiors. This is said to be accomplished by the use of at least one constricted portion formed in the sides of the permeating region of the hollow-fiber bundle.
U.S. Pat. No. 3,794,468 discloses a wound tubular diffusion membrane system wherein a kite winding type of approach is followed. This does not produce desired spacing and flow characteristics for such a device, in addition to being wasteful of fiber.
U.S. Pat. No. 3,413,095 discloses a disc membrane oxygenator woven glass fiber yarn is coated or impregnated with a relatively thick layer of silicone rubber.
There remains, therefore, a very substantial need for an efficiently functioning oxygenator and a method of making the same.